1. Field of the Invention
This invention relates to thermal control for microprocessors.
2. Description of the Related Art
With the increasing complexity of new microprocessors, thermal control becomes more challenging. Current microprocessors include extensive execution resources to support concurrent processing of multiple instructions. A drawback to providing a microprocessor with extensive execution resources is that significant amounts of power are required to run the microprocessors. Different execution units may consume more or less power, depending on their size and the functions they implement, but the net effect of packing so much logic onto a relatively small process chip is to create the potential for significant power dissipation problems.
In conventional thermal control systems, junction temperature (Tj) on a die is observed to ensure that it does not exceed an allowed maximum value to avoid reliability issues. When the junction temperature approaches the allowed maximum value, throttling may be activated to cool the microprocessor, resulting in a significant performance loss.
Detection of a maximum junction temperature violation may be accomplished by measuring the temperature of an area of a die close to the known hot spots. Some microprocessors use a thermal diode on the microprocessor die for temperature tracking. Temperature tracking can be used to activate some sort of throttling when the temperature level exceeds the maximum allowed value, or can be used to increase the microprocessor performance level (e.g., increase voltage/frequency) when the temperature level is low. It has been found that the current passing through the thermal diode is a function of temperature. Accordingly, a circuitry is provided, in at least some of the conventional thermal control systems, which is adapted to detect the amount of current passing through the thermal diode and to trigger throttling whenever the temperature on the die exceeds the allowed maximum value.
Currently used thermal diodes protect microprocessors from overheating situations, but may not be useful in mobile systems. In general, original equipment manufacturers (OEMs) of mobile systems prefer not to support thermal diode based throttling in normal operating conditions while running typical applications. Thermal diode throttling introduces non-deterministic behavior to mobile systems, something an OEM prefers to avoid. OEMs operate on the assumption that systems of the same type and having the same chip version behave similarly and provide the same benchmark score. Thermal diode based throttling creates a non-deterministic behavior since each chip has a different thermal response, leakage current, etc.